1. Field of the Invention
This invention relates to compatible polymer blends of styrene polymers and ethyl methacrylate polymers and composite systems thereof.
2. Description of the Prior Art
Polymer compatibility has been considered to be the exception to the rule since the beginning of pertinent studies, and incompatibility the rule. (Cf. Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Ed. Vol. 18, pg. 443-478 J. Wiley 1982). Prior studies of the compatibility of polystyrene appeared to confirm its general incompatibility with other polymers (Cf. R. J. Petersen et al., Polymer Preprints Am. Chem. Soc. Div. Polym. Chem. 10, 385 (1969)).
Very recently, however, some polyalkyl (meth)acrylates compatible with representatives of the polystyrene family have been discovered. Thus, polystyrene is compatible with polycyclohexyl (meth)acrylate up to the decomposition point (&gt;250.degree. C.). (Cf. U.S. Pat. No. 4,898,912; the state of the art is also evaluated thoroughly there). Copolymers of methyl methacrylate and ethyl methacrylate on the one hand, and higher alkyl esters of methacrylic acid on the other hand are also compatible with polystyrenes (cf. DE-A 37 30 025 (U.S. Pat. No. 4,897,441)). We found particularly good compatibility with polystyrene when the polymer also contained small proportions of cyclohexyl methacrylate (DE-A 37 30 026 (U.S. Pat. No. 4,892,909)).
Poly-.alpha.-methylstyrene also shows compatibility at room temperature with polymethyl methacrylate (PMMA), polyethyl methacrylate, and polybutyl methacrylate. Unlimited compatibility was found with polycyclohexyl (meth)acrylate (cf. U.S. Pat. No. 4,849,479). Poly(alkylstyrenes) (for example, those from the monomers p-methylstyrene, p-t-butylstyrene) very generally show compatibility with polyalkyl (meth)acrylates, when the condition is met that the side chains of the poly(alkylstyrenes) and the side chains of the polyalkyl (meth)acrylates show comparable Van-der-Waals volumes.
It is clear from the papers by Somani and Shaw, who studied the miscibility of poly(meth)acrylates with polystyrene using melt titration, that these types of polymers are incompatible for all practical purposes (miscibility only in the range of 10.sup.-5 to 10.sup.-6 parts by weight). The studies extended to blends of polystyrene with polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, poly-n-butyl methacrylate, and polymethyl methacrylate (cf. R. H. Somani, M. T. Shaw, Macromolecules 14, 1549 (1981)). One skilled in the art could not expect exceptions from the typical incompatibility behavior of the homopolymers of this class of polymer according to the state of the art. Immiscible polymer blends are opaque as a rule unless the components have approximately the same index of refraction. Blends of polystyrene and PMMA therefore show pearly opalescence that is sometimes used for decorative purposes (cf. O. Olabisi, L. M. Robeson & M. T. Shaw, Polymer-Polymer Miscibility, pg. 341, Academic Press 1979).
Both miscible and immiscible polymer systems have interesting aspects from the application point of view. Miscible polymer systems usually produce mechanical compatibility (cf. O. Olabisi et al., loc. cit. pg. 351). The resultant transparency of the system is also advantageous in blends that are inherently transparent. According to the findings discussed above, the state of the art did not lead to the expectation that blends compatible with polystyrene could be obtained in the range of poly(meth)acrylic esters of lower alkanols.